This invention relates to a liquid-filled vibration-isolating device used to support a vibration generating source such as vehicle engine for the purpose of vibration isolation.
A liquid-filled vibration isolator, in which a lower portion of a cylindrical body fitting and an attachment fitting disposed at an axis center are connected through a vibration isolating substrate made of a rubber elastomer, a diaphragm made of a rubber film is fitted and adhered above the cylindrical body fitting, liquid is contained in an inner chamber surrounded by the diaphragm and the vibration isolating substrate, a partition portion is interposed between the vibration isolating substrate and the diaphragm to partition a main liquid chamber on the attachment fitting side and a sub-liquid chamber on the diaphragm side, both liquid chambers are connected by an orifice on an outer circumference of the partition portion, an attachment fitting attached to the axis center of the vibration isolating substrate is connected to the vibration generating source side, the cylindrical body fitting is connected on the vehicle body support side, and the vibration damping function and the vibration isolating function are exhibited by the liquid flow effects of both liquid chambers and the vibration absorbing effects of the vibration isolating substrate by means of the orifice, has heretofore been known as a mount supporting a vibration generating source such as vehicle engine so as not to transmit its vibration to a vehicle body and the like.
As properties of the liquid-in vibration isolating device, it is an important factor to set sectional area and the like of the orifice for shake vibration on the outer circumference of the partition portion to the desired dimensions to obtain stable product properties without variation. Furthermore, it is desired to be able to reduce the dynamic spring rate in both relatively low frequency range (10 to 15 Hz) of shake vibration and the like and relatively high frequency range (100 to 200 Hz) of idle sound and the like from the viewpoint of vibration prevention or noise preventive effects as a mount for the vehicle engine and the like.
Accordingly, in addition to the liquid-filled vibration isolating device, another liquid-filled vibration isolating device is also suggested, in which the partition portion comprises a partition plate member made of an elastic film at its center portion and an orifice member disposed on the first sub-liquid chamber side of the partition plate member, a hollow space between the center plate portion of the orifice member and the elastic film is formed as a second sub-liquid chamber, independently of the orifice for shake vibration on the outer circumference which passes through the first sub-liquid chamber on the diaphragm side and between the sub-liquid chamber and the main liquid chamber, the orifice hole for idling sound is opened on the center plate portion from the first sub-liquid chamber to the second sub-liquid chamber, so as to reduce variation of the properties and also reduce the dynamic spring rate in both frequency bands of shake vibration and idling sound.
Incidentally, in the case of the configuration with two sub-liquid chambers described above, as the pressure of the main liquid chamber varies due to vibration, mainly vibration in the vertical direction, on the vibration generating source side such as an engine connected to the attachment fitting, inside liquid flows, liquid in the first sub-liquid chamber increases/decreases, and consequently the diaphragm at the upper portion constituting a chamber wall of the sub-liquid chamber approaches the partition portion and deforms in the direction of separation. At this time, when the diaphragm is displaced downwards greatly and approaches the partition portion, it is apprehended that the diaphragm comes into contact with the upper surface of the orifice member at the upper side of the partition portion and covers the orifice hole of the second sub-liquid chamber.
That is, the diaphragm is apt to displace at a closer portion to the center. Therefore, the diaphragm comes into contact with the center portion at first against the orifice member due to large displacement, and its contact area sequentially spreads around the center portion. If the center plate portion of the orifice member is flat, the diaphragm relatively quickly comes into contact all over the surface of the center plate portion.
Therefore, when largely displaced downwards, it is feared that the diaphragm covers the orifice hole for idling sound to disable its function. Furthermore, there is the possibility of scratching the diaphragm at the opening end of the orifice hole.
In order to settle the problems above, it is also considered to set the volume of the first sub-liquid chamber sufficiently large. If the volume of the first sub-liquid chamber is set sufficiently large, however, it is not preferable from the viewpoint of vehicle considerations and the like, because the vibration isolating device itself grows larger.
It is an object of the present invention to provide a liquid-filled vibration isolating device, equipped with second sub-liquid chamber connecting through an orifice hole for idling sound to the first sub-liquid chamber, apart from the first sub-liquid chamber described above, capable of maintaining its function properly without the orifice hole covered being the diaphragm, even if the volume of the first sub-liquid chamber is not increased.
As for a liquid-in vibration isolating device of the present invention, the lower portion of a cylindrical body fitting and an attachment fitting disposed at an axis center portion thereof are coupled through a vibration isolating substrate made of a rubber elastomer, a diaphragm made of a rubber film is bonded to the upper portion of the cylindrical body fitting to cover an opening at the upper portion, liquid is contained in an inner chamber between the vibration isolating device and the diaphragm, the inner chamber is partitioned into a main liquid chamber on the side of the attachment fitting and a first sub-liquid chamber on the side of the diaphragm by a partition portion, both liquid chambers are connected by a first orifice, wherein the partition portion comprises a partition plate member with an elastic film used for the center portion, and an orifice member disposed so as to push and come into contact with the circumferential portion of the elastic film to the partition plate member on the first sub-liquid chamber side, the first orifice is formed between the outer circumferential portion of the orifice member and the outer circumferential portion of the partition member, a hollow space between the center plate portion inward the pushing and coming into contact portion of the orifice member and the elastic film is formed as a second sub-liquid chamber, an orifice hole is opened on the center plate portion from the first sub-liquid chamber to the second sub-liquid chamber, the center plate portion of the orifice member is in a form of a convex with higher center portion faced toward the first sub-liquid chamber, and the orifice hole is provided at a low level portion of the center plate portion disposed eccentrically with respect to the device axis center.
According to the liquid-in vibration isolating device, since an orifice hole mainly for idling sound is provided on the first sub-liquid chamber and connected to the second sub-liquid chamber, in addition to the first orifice on the outer circumferential portion for shake vibration, the dynamic spring rate can be reduced in different frequency ranges of that for shake vibration (10 to 15 Hz) and relatively high range (100 to 200 Hz) for idle vibration and the like, respectively, thus effectively accomplishing vibration damping in a wide frequency range.
Especially, when the first sub-liquid chamber is reduced to lower pressure and contracted due to large downward displacement caused by vibration and the diaphragm approaches the partition portion, the center plate portion of the orifice member is in the form of a convexity with the center portion projected to the first sub-liquid chamber side, and the orifice hole is provided at a low level portion of the center plate portion disposed eccentrically with respect to the device axis center. Therefore, even being in contact with the center plate portion, the diaphragm hardly comes in contact with the orifice hole, or if it comes into contact with the orifice hole, it does not cover the orifice hole completely or earlier, allowing the function of the orifice hole to be maintained properly.
Further, since the diaphragm hardly come into contact with the orifice hole portion, the diaphragm is not broken even if the volume of the first sub-liquid chamber is small, thus durability can also be maintained properly.
As for the liquid-in vibration isolating device, it is preferable that the orifice hole is eccentrically positioned opposite to the interconnecting portion from the first orifice on the outer circumferential portion of the orifice member to the first sub-liquid chamber. This can prevent the first orifice and the orifice hole from interfering to each other, further allowing the properties to be stable.
As for the liquid-in vibration isolating device, since there is no difference in step on the upper surface of the center plate portion when the upper surface of the center plate portion of the orifice member is in the form of a convexity toward the first sub-liquid chamber side, the diaphragm naturally comes into contact, thus preventing the diaphragm from being damaged. Furthermore, when the lower surface of the second sub-liquid chamber of the center plate portion assumes a curved surface form corresponding to the upper surface, it can cope with large deformation of the elastic film which assumes a chamber wall of the second sub-liquid chamber opposite to the center plate portion, thus avoiding the elastic film from increasing local distortion.
As for the liquid-filled vibration isolating device, it is preferable that the interconnecting portion from the first orifice to the first sub-liquid chamber is opened at a place where the diaphragm is difficult to come into contact on the outer circumferential portion of the orifice member, and further that the interconnecting portion is opened so as to have an opening edge on the extended upper surface of the center plate portion of the orifice member.
This can properly maintain both functions of the first orifice for shake vibration and the orifice hole for idling sound in conjunction with blockage preventive effects of the orifice hole, without blocking up the interconnecting portion to the first orifice, when the first sub-liquid chamber is reduced to lower pressure or contracted during large displacement.
As for the liquid-filled vibration isolating device, it is preferable that the partition plate member of the partition portion is formed by vulcanization adhering the elastic film such as rubber to the center opening portion of the press molded metal plate, and that the orifice member is made up of the molded materials of metals such as aluminum and its alloys or ceramic or synthetic resin materials. This can raise dimensional accuracy of the orifice.